The ISP’s military has a twofold mission. Their first priority is border security; they are a primarily isolationist culture, and want nothing more than to be left alone. Access to their territory is tightly controlled, and anyone looking to bypass that control is punished harshly.
The second goal of the military is exploration. The Perseus Arm is largely uncharted, and potentially contains vast quantities of unclaimed resources. Exploring new territory is dangerous, and so the ISP expeditionary forces must be able to react to any sort of situation.